63 lines
1.8 KiB
Java
63 lines
1.8 KiB
Java
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package ciphers;
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import java.math.BigInteger;
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import java.security.SecureRandom;
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/**
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* Created by Nguyen Duy Tiep on 23-Oct-17.
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*/
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public class RSA {
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private BigInteger modulus, privateKey, publicKey;
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public RSA(int bits) {
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generateKeys(bits);
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}
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public synchronized String encrypt(String message) {
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return (new BigInteger(message.getBytes())).modPow(publicKey, modulus).toString();
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}
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public synchronized BigInteger encrypt(BigInteger message) {
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return message.modPow(publicKey, modulus);
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}
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public synchronized String decrypt(String message) {
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return new String((new BigInteger(message)).modPow(privateKey, modulus).toByteArray());
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}
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public synchronized BigInteger decrypt(BigInteger message) {
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return message.modPow(privateKey, modulus);
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}
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/** Generate a new public and private key set. */
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public synchronized void generateKeys(int bits) {
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SecureRandom r = new SecureRandom();
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BigInteger p = new BigInteger(bits / 2, 100, r);
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BigInteger q = new BigInteger(bits / 2, 100, r);
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modulus = p.multiply(q);
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BigInteger m = (p.subtract(BigInteger.ONE)).multiply(q.subtract(BigInteger.ONE));
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publicKey = new BigInteger("3");
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while (m.gcd(publicKey).intValue() > 1) {
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publicKey = publicKey.add(new BigInteger("2"));
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}
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privateKey = publicKey.modInverse(m);
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}
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/** Trivial test program. */
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public static void main(String[] args) {
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RSA rsa = new RSA(1024);
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String text1 = "This is a message";
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System.out.println("Plaintext: " + text1);
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String ciphertext = rsa.encrypt(text1);
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System.out.println("Ciphertext: " + ciphertext);
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System.out.println("Plaintext: " + rsa.decrypt(ciphertext));
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}
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}
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